Large shade trees look tough, yet long rainless summers test them. Sacramento summers bring months with little or no rain. Mature tree drought stress can build for years before the damage becomes obvious.
Catching the early signs gives a tree time to recover. The guidance below draws on University of California IPM pages.
Recognizing Mature Tree Drought Stress
UC IPM notes that irrigation during at least the drought season is required to maintain most urban landscapes in California. It calls inappropriate irrigation probably the most common cause of landscape plant damage. Too little and too much water can both cause harm.
Leaf Symptoms
According to UC IPM, inadequate soil moisture causes foliage to fade in color and wilt. Leaves may die along margins and tips. They may also drop early in the season.
Look at the upper and outer canopy first. Those parts often show stress before the interior does.
Slow Signs of Chronic Stress
Prolonged mild moisture deficit produces subtler effects. UC IPM lists dieback, fewer flowers and fruit, slower growth and smaller leaves. A tree may look thin rather than wilted.
Compare recent photos with older ones. A thinning canopy over several summers can point to chronic water shortage.
Pests That Follow Stress
Water deficit increases susceptibility to bark beetles and wood boring insects, UC IPM reports. These pests can kill weakened trees. Small holes, sawdust or sap on the trunk deserve a closer look.
Dry soil also raises the risk of cold injury. UC IPM explains that dry soil absorbs and radiates less plant warming heat.
When the Lawn Goes Away
Many trees depend on lawn irrigation for their water. UC IPM warns that if turf is removed or lawn watering is greatly reduced, nearby trees and shrubs will decline and possibly die. Grass conversions and watering cutbacks call for a separate plan for trees.
The post on why some lawns fail under mature trees covers the reverse problem.
Problems That Look Similar
Other disorders can mimic water deficit injury. UC IPM lists aeration deficit, frost, herbicide damage, root decay, salt injury, wind and boring insects among look alike causes. Overwatering can produce foliage symptoms resembling underwatering.
Check soil moisture before adding water. A trowel or soil probe shows whether the root zone is dry or soggy. The post on signs of too much water describes the other side.
Where Tree Roots Take Up Water
A UC IPM page on irrigation of trees and shrubs says about 90% of tree and shrub roots are usually in the top 3 feet of soil. Older plants in well drained soil tend to root deeper. Compacted or poorly drained soils lead to shallower roots.
How Deep to Water
UC IPM suggests checking that drip emitters and spray heads wet the entire root zone to a depth of about 12 to 18 inches. Frequency and volume vary with soil, species, season and system. Learn the soil type to guide decisions.
Light, frequent watering encourages shallow roots. Deep, less frequent watering supports deeper rooting.
Where to Apply Water
Once a tree is established, UC IPM advises applying water around the drip line beneath the outer canopy. Keep water away from the trunk so the root collar stays dry. Soaker hoses or drip rings placed under the canopy edge work for many yards.
Mulch helps the soil hold moisture. Keep it away from the trunk, as the post on mulch volcanoes explains.
Timing Within the Day
UC IPM names early morning or just before dawn as generally the preferred time to irrigate. Watering around dawn reduces evaporation and shortens the time foliage stays wet. Wind and water pressure also tend to favor predawn watering.
Follow the irrigation rules of your water supplier. City of Sacramento customers have assigned watering days, with exemptions for drip and soaker hoses.
Weather and Demand
Tree water demand rises in hot, sunny, windy and dry weather. Heat waves can push a borderline tree into visible stress. Extra deep watering ahead of a heat spell can help.
Smart controllers that use soil moisture sensors or weather data can adjust schedules. Manual controllers need seasonal changes by hand.
Trees on a lawn zone may need their own drip or bubbler zone. A separate zone lets trees get deep, infrequent water while lawn gets shorter runs. Ask an irrigation contractor whether existing valves and pipes can support an added tree zone without major trenching.
A Simple Monthly Check
Walk around each large tree once a month during summer. Look at leaf color, leaf size and any early drop. Note new dead twigs at branch tips.
Dig a small hole near the drip line and feel the soil a few inches down. Write down what you find along with the date. A short record shows trends that a single visit misses.
Soil Type and Water Holding
Clay soils hold water longer yet absorb it slowly. Sandy soils take water quickly and dry out faster. UC IPM suggests learning soil characteristics from NRCS soil survey maps or the UC SoilWeb tool.
Run water slowly on clay so it soaks in rather than running off. Cycle and soak scheduling breaks one long run into shorter ones.
Pruning a Stressed Tree
Heavy pruning removes leaves a stressed tree needs for food. Topping in particular creates new problems. The post on why topping a tree creates new problems explains the risks.
Safety Concerns
UC IPM notes that declining and dead trees can be hazardous where limb drop or trunk failure could injure people or damage property. Large dead limbs over roofs, paths or play areas deserve prompt attention. An ISA certified arborist can assess risk.
Street trees in Sacramento may fall under city care. Contact City of Sacramento Urban Forestry about trees in the planting strip.
Planning for the Long Term
Mature tree drought stress often follows a change such as lawn removal or a new watering schedule. Plan tree watering at the same time as any yard change. More tree topics sit in the tree health category.